Parkinson's disease is a condition in which parts of the brain become progressively damaged over many years.
The main symptoms of Parkinson's disease are:
A person with Parkinson's disease can also experience a wide range of other physical and psychological symptoms.
These include:
See a GP if you're concerned that you may have symptoms of Parkinson's disease.
They'll ask about the problems you're experiencing and may refer you to a specialist for further tests.
Find out more about diagnosing Parkinson's disease
Parkinson's disease is caused by a loss of nerve cells in part of the brain called the substantia nigra. This leads to a reduction in a chemical called dopamine in the brain.
Dopamine plays a vital role in regulating the movement of the body. A reduction in dopamine is responsible for many of the symptoms of Parkinson's disease.
Exactly what causes the loss of nerve cells is unclear. Most experts think that a combination of genetic and environmental factors is responsible.
Most people with Parkinson's start to develop symptoms when they're over 50, although some people with the condition first experience symptoms when they're under 40.
Men are slightly more likely to get Parkinson's disease than women.
Although there's currently no cure for Parkinson's disease, treatments are available to help reduce the main symptoms and maintain quality of life for as long as possible.
These include:
You may not need any treatment during the early stages of Parkinson's disease, as symptoms are usually mild.
But you may need regular appointments with your specialist so your condition can be monitored.
As the condition progresses, the symptoms of Parkinson's disease can get worse and it can become increasingly difficult to carry out everyday activities without help.
Many people respond well to treatment and only experience mild to moderate disability, whereas the minority may not respond as well and can, in time, become more severely disabled.
Parkinson's disease does not directly cause people to die, but the condition can place great strain on the body, and can make some people more vulnerable to serious and life-threatening infections.
But with advances in treatment, most people with Parkinson's disease now have a normal or near-normal life expectancy.